200G Unusable free disk space, with win7 but no grub boot, long story!

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Posting the fdisk output as suggested above would be a good first step.

I plugged in my parted magic DVD, and deleted the mint, just like that!

Since you were booting both windows and the previous Mint with Grub and almost all Grub files needed to boot were on the Mint partition, you have rendered the machine unbootable as you found out. I'm not sure where the 30270 bytes are coming from and why you didn't use the 200GB of free space you have. Posting the partition information requested might help someone to help you.

You must format new partitions with a file system before you can use
them. You can do this with the appropriate mkfs command.
For example, this command formats the fifth partition on the first disk
with the ext4 file system.

You have three windows partitions are your 500GB drive and no Linux. During the installation of Linux Mint, you should see an Installation Type window where you can select free or unallocated space to create a new partition or new partitions. Click on free/unallocated space in the main window, click the Add tab below and set the size, filesystem type and mount point for each partition. Also click the Format box. If you want multiple partitions, make sure you pay attention to the size of the partition in the Edito partition window. The default for Device for bootloader installation should be "/dev/sda" which should be unchanged. If the install is successful, you should be able to boot Mint and windows. You won't need to use the mkfs.ext4 command as this will be done in the Edit partition window mentioned above.

I keep that iso on hand like a wrench in a toolbox. I put it on uSB with Unetbootin and use it instead of Mint. Why? Because Mint live DVD did not come with Gparted.
At least mine did not. All mine had was Disk Usage Analyzer.